Blend between any pair of five vowels using the filter position slider in either of the available modes:
Frequency - Moves the cutoff frequencies of a single bank of formant filters between the two selected vowel sounds to get the classic modulated formant filter sound
Blend - Blends two parallel banks of formant filters without changing their cutoff frequencies for a more subtle effect
The Air control can help brighten up dull sounds by bringing in additional formant filters at higher harmonics.
Built in LFO and envelope follower
You can always use parameter automation to modulate the filter position, but Songbird also includes two more options:
LFO with multiple wave shapes and tempo sync
Envelope follower which responds to the incoming audio according to the attack and release controls, applying positive or negative modulation as set by the amount control
Songbird is an open source project released under the GPL
I make every effort to ensure these products are reliable and great to use however I am only a single developer, so can't exhustively test every platform and use case.
As such all products are provided without any warranty or promise of fitness for purpose.